NIST zero-energy house gives back to the grid

Over the first six months in their special, new, four-bedroom home in suburban Maryland, the Nisters, a prototypical family of four, earned about $40 by exporting 328 kW-h of electricity into the local grid, while meeting all of their varied energy needs.

And these virtual residents of the Net-Zero Energy Residential Test Facility (NZERTF) on the campus of the National Institute of Standards and Technology (NIST), about 20 miles north of Washington, D.C., didn't have to skimp even a bit on any of the creature comforts of 21st century living. Their amenities ranged from indoor temperatures maintained between 21.1 and 23.8 C (70 to 75 F) to a complete array of modern-day kitchen and laundry appliances, and from personal computers, a video gaming system, and two TVs to a pair of stereos, a hairdryer, and curling and clothes irons.

Both a laboratory and a home, the 2,700-square-foot (252-square-meter) NZERTF is a two-story, four-bedroom, three-bath house that incorporates energy-efficient construction and appliances, as well as energy-generating technologies such as solar water heating and solar photovoltaic systems. There, NIST scientists and engineers and their collaborators will develop and validate measurement and test methods for evaluating energy-efficient designs, materials and technologies.

Over the course of a year, the facility is designed to produce at least as much energy as it consumes. On July 1, 2013, a research team led by NIST engineer Hunter Fanney launched a year-long trial to determine whether NZERTF, as originally designed and built, meets these net-zero-energy expectations, despite the vagaries of local weather. That's when the Nisters—computer-simulated versions of two working parents and two children, ages 8 and 14—"moved in."

Though daily routines and energy-consuming habits are scripted and imitated by computer, this virtual clan behaves like the average family, based on standard occupant profiles developed by the Department of Energy. The Nisters bathe, shower, cook, turn on lights when they enter rooms, do the laundry, and relax by watching TV, listening to music, posting on Facebook, or playing video games. Computers even control devices that mimic the heat and moisture of the virtual family's breathing and perspiring.

"When it comes to energy use and production, nothing is going unmeasured," Fanney explains. "The house has more than 500 sensors to track the energy consumption of every single device. We are gathering a lot of valuable information that will be put to good use when we progress to the next stage and use our net-zero energy lab to develop improved test methods and performance metrics for high-efficiency and alternative-energy devices and systems."

As of December 31, 2013—the halfway point in the initial trial run—the NZERTF generated an energy surplus of 328 kW-h, roughly the amount of energy that a dishwasher uses over one year. From July through October, the facility registered monthly surpluses. In November and December, when space-heating demands increased and the declining angle of the sun reduced the energy output of photovoltaic system, NZERTF ran monthly deficits.